I deeply recommend VÖNER! Vegan Döner Kebap: http://www.voener.de
Boxhagenerstraße 56 in Friedrichshain, close to the Ostkreuz S-bahn-station.
Not to be missed.
If you like falafel Berlin is a great town, just make sure you don't get the microwaved falafel that some lazy bastards sell.
Perharps the most delicious falafel joint is Dada Falafel at Linienstrasse 132, close to the Oranienburger Straße S-Bahn-station.
Yellow Sunshine is not a very cozy restaurant but their menu is not to be underestimated. Download it here: http://www.yellow-sunshine.com/speisekarte_A3_eng.pdf
If you're out partying, it's almost 03:00 and you want something else than falafel or just a pita bread with salad (sometimes refered to as vegetarischer döner) then go to Kreuzburger and get a decent Tofu-burger.
There is one Kreuzburger joint in Kreuzberg and one in Prenzlauer Berg: http://www.kreuzburger.de